In the literary works of J. R. R. Tolkien, the House of Isildur was the Royal House of Arnor, Arthedain, Cardolan, Rhudaur and, much later, Gondor

Reunited Kingdom

The Reunited Kingdom of Arnor and Gondor is a fictional realm from J. R. R. Tolkien's Middle-earth.When Aragorn became King of Gondor at the end of the War of the Ring, he was also the descendant of the Kings of Arnor, and by right he was crowned High King of both Arnor and Gondor and Reunited the...

 The house was descended from Isildur

Isildur

Isildur is a fictional character in J. R. R. Tolkien's legendarium. He appears in the author's books The Lord of the Rings, The Silmarillion, and Unfinished Tales....

, elder son and heir of Elendil the Faithful

Elendil

Elendil is a fictional character in J. R. R. Tolkien's legendarium. He appears in The Lord of the Rings, The Silmarillion and Unfinished Tales....

. Although the North-Kingdom was ended in the year 1975 of the Third Age

Third Age

The Third Age is a time period from J. R. R. Tolkien's Middle-earth fantasy writings. The history of Middle-earth is to be taken fictionally as a history of the real Earth....

, the House of Isildur was maintained as the Chieftains of the Dúnedain, the wandering folk that the Dúnedain of Arnor became, until the time of Aragorn II and the War of the Ring

War of the Ring

In the fictional high fantasy-world of J. R. R. Tolkien, the War of the Ring was fought between Sauron and the free peoples of Middle-earth for control of the One Ring and dominion over the continent. The War of the Ring took place at the end of the Third Age. Together with the Quest of Mount Doom,...

, after which, Aragorn claimed the Crown of Gondor

Gondor

Gondor is a fictional kingdom in J. R. R. Tolkien's writings, described as the greatest realm of Men in the west of Middle-earth by the end of the Third Age. The third volume of The Lord of the Rings, The Return of the King, is concerned with the events in Gondor during the War of the Ring and with...

 as the direct descendant of Elendil. After Aragorn, the House of Isildur became the House of Telcontar

House of Telcontar

In the fictional universe of J. R. R. Tolkien, the House of Telcontar, previously the House of Elendil, is the Royal House of the Reunited Kingdom of Arnor and Gondor...

 and ruled the Reunited Kingdom for generations.

It was the pride and wonder of the Northern Line that, though their power departed and their people dwindled, through all the many generations the succession was unbroken from father to son. ... But in Aragorn the dignity of the kings of old was restored

However in Cardolan, the Line of Isildur died out and was replaced by local noblemen. Cardolan recognised therefore the overlordship of Arthedain, though Rhudaur gave its loyalty to the Witch-king

Witch-king of Angmar

The Witch-king of Angmar, also known as the Lord of the Nazgûl and the Black Captain among other names, is a fictional character and a major antagonist in J. R. R. Tolkien's Middle-earth fantasy writings. In Tolkien's novel The Lord of the Rings, he is the chief of the Nazgûl , the chief servants...

 and Angmar

Angmar

Angmar is a fictional kingdom in J. R. R. Tolkien's continent of Middle-earth.-Synopsis:Angmar was founded in in the far north of the Misty Mountains by the evil Lord of the Ringwraiths, who became known as the "Witch-king of Angmar"...

 which led to long hostilities, although most of the Dúnedain

Dúnedain

In J. R. R. Tolkien's legendarium, the Dúnedain were a race of Men descended from the Númenóreans who survived the sinking of their island kingdom and came to Eriador in Middle-earth, led by Elendil and his sons, Isildur and Anárion...

of Rhudaur left for Cardolan and Arthedain.